Process for preparing cellulose



Patented Nov. 6, 1934 I UNITED STATES,

PATENT'HO'FFICE rnocnss non PREPARING cE LULosE' No Drawing. Application April 11, 1929, Serial No. 354,443. Renewed April 3, 1934- Claims.

This invention relates to a process for preparing cellulose and more'particularly to the conversion of wood in the form of chips to chemical pulp such as is used in the manufacture of paper 5 and the like.

In forming chemical monly placed in a digester and extensively cooked with digesting liquors until the chips are thoroughly penetrated, thus decomposing the lignin,

10 tannins, sugars, etc. The cooking requires a considerable period of time because of the slow penetration of the digesting liquors to convert the entire chip to the desirable cellulose, resulting in a degradation of the cellulose, especially of thatadjacent to the surfaces of the chips, and if the chips happen to contain a high content of tannins the cooking is carried out to the extent that as much as 60% of the dry weight of the original chips is removed. After sufficient cooking the chips are blown out of the digester by the internal pressure in the digester, converting the chipsto a pulpy mass of fibres, which are'thereafter thor- I for converting woodchips into chemical pulpwithout degrading or removing any of the cellulose.

In attaining these objects the chips are thoroughly saturated with water or other incompressible medium and thereafter placed in a high. Steam is admitted to the pressure chamber. chamber under a pressure usually from 500 to 1000 pounds per square inch; which subjects the chips to a high external pressure. This high external pressure is suddenly removed by the openingof a large aperture or door in the pressure chamber and the saturating medium such as water or other incompressible medium within the chips suddenly changes its state or expands or explodes, shattering or destroying the original chips, converting them into a finely divided mass of fibres or pulp. This mass of fibres or pulp is blown out wardly from the pressure chamber and is thereafter leached in a series of vats in which counter currents of water are circulated so as to remove the tannins and sugars which in some cases will amount to as much as 20% of the dry weight of the wood. The tannin liquors from these vats are thereafter evaporated to desired concentration or pulp wood chips are comthe evaporating may-becontinued to form the tannins into a dry powder.

The finely divided mass ,of fibres or pulp is thereafter treated "preferably ina-digesterof any well known design and is cooked with digesting liquors to remove the encrusting lignins. The process of digestion may be any .well known process such as the kraft, soda, sulfite or similar delignifying treatment. Because of the finely divided state of the mass of fibres the time usually consumed inpenetrating. the chips with the digesting liquor is greatly reduced and only a slight amount ofcooking is required. Also a very small amount of the active chemicals of the digester liquors is thus consumed as approximately 20% of the non-cellulose-material such as tannins and sugars has been removed before the pulpy-mass was treated in the digester: and also because the slight cooking required in the digester does not degrade the cellulose. This digesting step not only reduces the time element, the consumption of chemic'als and power, but. also permits the greater quantity of material being processed in a given piece of equipment and produces a higher yield of cellulose of a higher quality since less degradation of cellulose occurs due to the shorter period of cooking and the reduced concentration of chemicals which may be employed.

After the waste liquors have been removed from the pulp it is washed and screened and thereafter acidulated by steeping it in sulphuric acid at approximately 5% concentration using ten parts of brightness considerably increased as compared to.

larly with reference to the conversion of wood to chemical pulp and the like, the invention is not confined thereto but is intended to cover any other uses or modifications or reversal of steps in carrying out the process within the scope of the appended claims.

I claim:

1. The process of treating wood to form chemical pulp which consists in forming the wood into chip form, disrupting the chips into pulp, then washing the tannins and sugars from said previously formed pulp, then digesting said pulp to remove encrusting lignins, acidulating said pulp, and thereafter bleaching the same.

2. The process of treating wood to form chemical pulp which consists in forming the wood into chip form, disrupting the chips by subjecting the same to high fluid pressure in excess of 200 pounds per square inch and suddenly releasing the high fluid pressure on the whole mass to form a pulp, then washing the tannins and sugars from said previously formed pulp, then digesting said pulp to remove encrusting lignins, acidulating said pulp, and thereafter bleaching the same.

3. The process of treating wood to form chemical pulp which consists in forming the wood into chip form, saturating said chips with an incompressible medium, disrupting said chips by subjecting the same to high fluid pressure in excess of 200 pounds per square inch and then suddenly releasing the high fluid pressure on the whole mass to form a pulp, then washing the tannins and sugars from said previously formed pulp, digesting said pulp to remove encrusting'lignins, acidulating said pulp, and thereafter bleaching the same.

4. The process of producing paper pulp from wood comprising forming the wood into separated small pieces giving a relatively large surface area and reducing the time of penetration, subjecting said material to digestion for a reduced period of time with only a slight amount of cooking, and thereby producing a high yield of cellulose'of high quality by avoidance of degradation of the cellulose fibres originally present in the wood.

5. The process of producing paper pulp from wood comprising forming the wood into separated small pieces giving a relatively large surface area and reducing the time of penetration, washing said material to remove tannins and sugars, subjecting said washed material to digestion for a reduced period with only a slight amount of cooking, giving said material a second wash, acidulating said material and then bleaching it so as to produce a high yield of cellulose of high quality by avoiding degradation of the cellulose fibres originally present in the wood.

FREDRIICH OLSEN. 

